Genetically enhanced microorganisms that make ethanol or other biofuels through photosynthesis can be cultivated in photobioreactors, in which cultures of the microorganisms are provided with carbon dioxide and sunlight. Operation of a photobioreactor entails inoculating the photobioreactor with microorganisms in liquid media, such as saline water or fresh water, to which nutrients and other growth agents are added.
Access to saline water typically is more prevalent and less expensive than access to fresh water. To minimize cost, a supply of saline water may be sourced, for example, from seawater or from groundwater drawn from a saline aquifer.
Water drawn from uncontrolled sources such as seawater or groundwater may contain microorganisms that are undesirable for placement within a closed photobioreactor. Undesirable microorganisms include fungi, bacteria, viruses, spore forms and other microorganisms that, if added to a culture in a photobioreactor, may outcompete the genetically enhanced microorganisms in the culture and/or consume product made by the genetically enhanced microorganisms.
Various approaches to treating water are the subject of, for example, WO/2014/124357; U.S. Pat. App. Pub. No. 2010/0116647; WO/2008/037324; U.S. Pat. App. Pub. No. 2004/0129645; U.S. Pat. App. Pub. No. 2008/0035580; U.S. Pat. App. Pub. No. 2004/0061069; U.S. Pat. App. Pub. No. 2007/0136834; U.S. Pat. App. Pub. No. 2012/0312757; U.S. Pat. App. Pub. No. 2004/0226893; U.S. Pat. App. Pub. No. 2005/0155539; WO/2003/106350; U.S. Pat. App. Pub. No. 2011/0250604; U.S. Pat. No. 5,264,136; U.S. Pat. No. 5,888,428; U.S. Pat. No. 7,052,601; U.S. Pat. No. 6,986,323; U.S. Pat. No. 5,250,177; U.S. Pat. No. 5,151,250; U.S. Pat. No. 3,459,528; Perrins et al., “Ozonation of seawater from different locations: formation and decay of total residual oxidant—implications for ballast water treatment”, Mar. Pollut. Bull. 2006 September; 52(9):1023-33; epub 2006 Mar. 15; Nielsen, “Control of Ballast Water Organisms with a Seawater Electrochlorination and Filtration System”, a thesis submitted in partial fulfillment of the requirements for the degree of Master of Science, University of Washington 2006; Oemcke, “The treatment of ships' ballast water”, EcoPorts Monograph Series No. 18 (Ports Corporation of Queensland, Brisbane), 1999, 102 pp.; Det Norske Veritas, “Technical Report, Barber Ship Management, Ballast Water Treatment By Ozonation—Corrosion”, Report No. 2001-0522, Rev. No. 1, 2001; and Sciortino et al., “Fishery Harbour Manual on the Prevention of Pollution—Bay of Bengal Programme”, BOBP/MAG/22, Madras, India 1999.
A need exists for a system and method of neutralizing and removing microorganisms from water drawn from uncontrolled sources to a degree that is satisfactory for use with cultures of genetically enhanced microorganisms in closed photobioreactors. Treating water for this purpose using on-demand production of sterilizing agents, thereby avoiding on-site storage of potentially toxic chemicals, is also advantageous.